My wife has stretch marks on her stomach, my wife isn't coming for tes

Hi sir, I got married 7 months back, I found stretch marks on my wife abdomen. She said she got them due to wait loss. I didn't question her after that. Later I found my wife is cheating me. I don't have any evidence for that. I asked her to come for medical check up to identify whether she was pregnant before marriage. She is not coming for medical check up. What should I do. Since she is not honest to me, I would like to take divorce from her. I would like to file a cheating case on her family. Kindly give me your valuable suggestion. Thank you.